#1 Euphorbia lathyrus
#2 Brunnera [probably the basic form, macrophylla, which has forget-me-not like flowers in spring, and is a self-seeding thug]
#3 Possibly the native avens, usually a weed. A flower would help to identify it properly, Also what the plant looks like at soil level.
#4 Certainly a form of knotweed, and since the flowers are white, probably the notorious Japanese form.
#5 A begonia, but which will take a lot of searching. There are hundreds.